Wave-signal selector system



July 4, 1950 B. F. TYsoN 2,513,761

WAVE-SIGNAL SELECTOR SYSTEM Filed June 14, 1945 2 sheets-snee*b 1 n g2 al) j 22 al d f? -f 'T f ,zo Si 29 1g u E ya E E g; x Yi?- i? WAVE-SIGNAL EL y y?? y 85; TRANsLATlNG 25 7 APPARATUS Hum |5v 23 24 img kw m INVENTOR. BENJAMIN F. TYSON Flea Jllly 4, 1950 B. F. rYsoN WAVE-SIGNAL SELECTOR SYSTEM 2 Sheets-Sheet 2 Filed June 14, 1945 FIG. 4

Patented July 4, 1950 UNITED STATES PATENT OFFICE WAVE-SIGNAL SELECTOR SYSTEM Benjamin F. Tyson, Bayside, N. Y., assigner, by mesne assignments, to Hazeltine Research, Inc., Chicago, Ill., a corporation of Illinoisl Application June 14, 1945, serial No. 599,372

16 Claims. 1

The present invention relates to wave-signal selector system's and, particularly, to such systems of the resonant wave-guide type tunable over a given relatively Wide frequency range of high-frequency Wave signals. In greater particularity, the invention relates to such tunable selector systems having approximately constant band Width when tuned to resonate at any selected Wave-signal frequency in a relatively Wide.`

further to select the desired wave signal to the exclusion of the undesired wave signals.l

Such wave-signal selector systems f usually translate with appreciable amplitude all Wave signals having frequencies lying within a predeterm'ined continuous frequency band, limited by an upper and a lower cutoff frequency, and substantially reduce the amplitudes of Wave signals having frequencies outside of that band. The group of Wave-signal frequencies translated by the selector is called the pass band of the latter and may be either narrow or Wide as desired for a specific application. Where the selector system is of the fixed-tuned type, as in the intermediate-frequency stages of a wave-signal receiver, a desired band-pass characteristic for the system may be readily provided by suitable design and adjustment of the system components. Tunable selector systems, on the other hand, may readily be provided Withv a desired bandpass characteristic when tuned to one Wavesignal frequency but require more complicated circuit arrangements or a particular manner of variation of related circuit components thereof, or both, Where it is desired that the band Width of the system remain approximately constant with. tuning of the system over a range of such frequencies.

The problems. encountered in the design and adjustment of a constant-band-width tunableV selector system have heretofore been generally capable of solution in relatively low-frequency wave-signal. selector systems.r This is because such systems employ lumped inductors and capacitors which may be designed and constructedv to have some particular law of variation with tuning made necessary to maintain an approximately constant band Width for the selector system. High-frequency Wave-signal selector systems employing resonant Wave guides, however, have no such lumped circuit components but rather rely for their resonanceV phenomena upon distributed'inductances and capacitances of the,

Wave guide. The term wave guide applies to a system' of conductive surfaces which act as the boundary of an electric wave and have the ability of directing the propagation of such Waves, much as the rigid Wall of a speaking tube is used to guide sound by preventing the sound from spreading into space. Wave guides may take the form of one or more conductors in open space, one conductor enclosed within but electrically insulated from a second conductor as in a conventional coaxial transmission line, or may simply comprise a single hollow conductor capable of.

propagating the electric wave through the intef rior thereof.

For many applications, it would be desirable to provide a resonant wave-guide type of wavesignal selector system adjustably tunable over a given relatively Wide frequency rangev and having a band-pass characteristic of any Width desired, yet one the band Width of Which remains approximately constantover the tuningrrange of the system. It would further be desirable that such selector systems involve no complicated circuit arrangement or peculiar mode of adjustment with tuning, but rather, it is desirable that they be simple both electrically and mechanically.

It is an object of the present invention, therefore, to provide a Wave-signal selector system of the Wave-guide type, and one adjustable over a given relativelyv wide frequency range, which y possesses the desirable characteristics last-mentioned.

It is a further object of the invention to provide a constant-band-width wave-signal selec-Y tor system of the Wave-guide type which is f adaptedto be coupled either capacitively or inductively as desired' to associated Wave-signal l band-pass characteristic for the system,

able over a given relatively Wide frequency range,`

comprises a resonant Wave guide.. having a frequency pass band of predetermined band width, adapted to be coupled to an electrical device and means for adjusting the effective electrical length of the wave guide to tune the selector system over the aforesaid frequency range.` The selector includes wave-signal coupling means electrically coupled to the wave guide at a predetermined point along the length thereof and adapted to provide coupling between the wave guide and a resistance component of impedance provided by` the device which is effective to increase the aforesaid band width of the wave guide. The location of the coupling point is so selected that the wave guide has, for any given value of the resistance component of impedance and when tuned over the aforementioned frequency range, approximately maximum band width at substantially the mean frequency of the frequency range; The location of the coupling point is determined by the relation mi; M 4 c an c ,p

where w represents the angular frequency in radiansv persecond of the signal inthe wave guide at resonance, c represents'the velocity of light in centimeters per second, m represents the distance in centimeters between the coupling point and one end of the wave guide, and p has a value determined 'by thev characteristics of 'the wave guide and the device, whereby the selector system has for a constant value4 of the resistance component of impedance a substantially constant bandwidth for any `adjustment within the range.`

thereof, reference is had to the following description taken in connection with the accompanying drawings, and its scope will be pointed out in the appended claims.

Referring now to the drawings; Fig. 1 illustrates, partly schematically, a complete wave-signal translating' system which utilizes a selector system embodying the present invention in a particular form; Figs.,1a. and 1b, respectively, represent equivalentI circuit diagrams of a selected portion and of the'entire selector-system of Fig. 1; Fig. '2 schematically represents a selector system of the Fig. 1 type embodying a modified form of the invention;` Fig. 3 illustratesa selector system embodying anadditional 'modified form of the invention; Figs. .4 and' schematically represent selector systemsfembodyingyet other forms of the invention; and Fig. 6 illustrates an embodi- For a betterunderstanding of the present inn vention, together with other and further objects 4 tem includes an antenna I and conductive disc II, providing a ground plane for the antenna, which are coupled by an electrical device, in particular a coaxial transmission line I2 to a wavesignal selector system I3, presently to be described in greater detail. The selector system I3 is coupled by a coaxialtransmission line I4 toa wavesignal circuitofq'a Wave-signal translating apparatus I5 which may, for example, be a wavesignal receiver or a wave-signal transmitter.

It will be understood that the various units just described may, with the exception of the selectorsystem i3, be of a conventional construction and operation, the details of which are well known in the art-,rendering a further detailed description thereof unnecessary. Considering briefly the operation of the wave-signal translating system as a whole, and neglecting for the moment the detailed operation of the selector ment of the invention as. applied to a rectangular Wave guide. y

Referring lnow more particularly to Fig. y1 of the drawings,v there is represented, partly schematically, `Va complete wave-signal translating system which utilizes a wave-signal selector system embodying the presentfinvention in a particular form. The wave-'signal translating syssystem I3 presentlyv to be described, assume for purposes of the present description that the apparatus I5 is a wave-signal'receiver. Wave signals received by the antenna system Ill, II are translated bythetransmission line i2 to the wavesignal selector system, I3 Iwhich is tunable to select a desired received wave signal to ythe exclusion of undesired received wave signals; The

selected received wave signal istranslated by the selector system I3 and the transmission line It to the wave-signal translating apparatusl I5 where the wave signal is `suitably amplied and the modulation components thereof derived and utilized.

Referring now more particularly to theportion of the Wave-signal translating system embodying the present invention, the wave-signalselecltor system VIii-which isadjustable over al given relatively wide frequency range, includes a plurality of resonant wave guides I6, I7, each of the coaxial transmission-line type havingcoaxially supported outer and innerv conductors I8, I9 and 20, 2I, respectively. Bya coaxial line type of wave guide is meant, in its broad concept, one having an inner conductor. substantially surrounded byan outer conductor which acts as an electromagnetic-wave shield for the former, the two conductors cooperating totranslate velectromagnetic energy Y therebetween and longitudinally thereralong. Each of these transmission lines has an eifective Aelectrical length equal approximately to an odd number of quarter-wave lengths at the lowest frequency in the aforementioned'frequency rangefand is electrically open at one end 22 thereof to provide at the open end a fixed region of maximum wave-signal impedance. Each of the transmission lines IIS and I 'I includes means for. adjusting theeffective electricallength thereof to-tune the selector system I3 overfthe aforementioned frequency range. `In particular, this means comprises means co-operating with 'another reg-ion of the transmissionline spaced from the region'ZZ of maximum wavesignal impedance for providing a second adjustable region of minimum wave-signal impedance. This means comprises forthe line, IB a conductive piston member 23. having resilient contact fingers conductively engaging the outerl conductor I8 and inner conductor I9, thus to short-circuit the transmission line I6 and terminate the electromagnetic field thereof at the region of the member 23. A similar conductive piston member 24 is provided for the line I'I., T he members 23 and 24 are movable longitudinally of their respective lines to; adjust the effective electrical lengths thereof to an odd number of quarter-wave lengths at any frequency within the aforementioned frequency range. The members23 and 24 are mechanically coupled by a tuning member 25, WhiCh may be either of metal or insulating material, to effect simultaneous tuning of thelines I6 and Il to a desired wave-signal frequency.

'Ihe Wave-signal selector system I3 also includes a plurality of wave-signal coupling means electrically coupled to individual ones of the transmission lines I6 and I'I at a first predetermined point along the length of each thereof and adapted to provide coupling between the wave guides and individual resistance components of impedance which are effective to increase the band width of each transmission line. This means for line IB comprises a conductive element 26 secured to the inner conductor of the transmission line I2 and lying within the transmission line I6 to be capacitively coupled, as indicated by the broken lines, to theinner conductor I9 thereof. A similar conductive elementY 21I is provided for line I'I and is capacitively coupled to the inner conductor 2I thereof and connected to the inner conductor of the-transmission line III. The location of each of these first coupling points is selected a fixed distance q from the open ends 22 of the lines I6 and II, and thus, a xed distance from the regions of maximum impedance thereof. The value of the distance a is so selected that each of the wave guides has for any given value of its individual resistance component of impedance and when tuned over the frequency range, approximately maximum band width at substantially the mean frequency of the aforementioned frequency range. Under the conditions stated, each line has for a constant value of the resistance component 'of impedance coupled thereto a substantially constant band width when tuned to resonate at any frequency within the range.

The wave-signal selector system I3 also includes wave-signal coupling means electrically, and particularly capacitively, coupling the transmission lines I6 and I1 at a second predetermined point along the length of each thereof. This means comprises a conductive element 28 lying within the transmission line I6 and capacitively coupled, as indicated by the-,broken lines, to the center conductor I9 thereof andy a conductive element 29 lying Within the line I1 and capacitively coupled tothe center conductor 2I thereof, the elements 28 and 29 being connected together by conductive member 30 which should have the shortest practicable length. The locations of the last-mentioned coupling points are also selected a fixed distance b from the open ends ,22 of the lines, and thus also a fixed distance from the regions of maximum impedance thereof. The distance br is so selected that the selector system has, when tuned over its frequency range, approximately maximum over-all band width at substantially the mean frequency of the aforementioned` frequency range. Under the conditions last stated, the selector System I3 also has a substantially constant over-all band width when tuned to resonateat any frequency within the range.

Adequate shielding of the transmission lines.V I6 and I'I is effected by extending the outer conductors thereof a small distance d and by closing the extended end of the outer conductors by a conductive plate 3|.

In considering the operation of the selector system just described, reference is made tot Fig. la

which represents the equivalent circuit diagram of the transmission line I6. The antenna system of the Fig. 1 arrangement is represented in conventional manner in Fig. la in that it is indicated as matched to the transmission line I2 so that there is coupled to the line I6 only a resistor Ra, having a value of resistance equal to the characteristic impedance of the transmission line I2. The capacitive coupling between the conductive element 26 and the inner conductor I9 of the line I6 is represented in Fig. 1a by the condenser Ca. For convenience of reference, it will be assumed that the conductive element 26 forms one plate of a condenser Ca. the other plate of which is connected to a tap point a: on the inner conductor I9 as indicated by broken lines in Fig. 1.

In the following mathematical analysis of the selector system operation, it is assumed that the capacitive reactance of the condenser Ca is appreciably greater than the value of thev resistor Ra or, in other words, that it is appreciably greater than the characteristic impedance of the transmission line I2. The effective shunt capacitance at resonance of the line I6 is represented in Fig. lo. by a lumped capacitance C1 having a value equal to one-half the total capacitance of the line at resonance. It can be shown that the value of the capacitance C1 is given by the relation: 3.0

Where w=angular frequency in radians per second (2n-f) of the line I6 atv resonance. K=the characteristic impedance of the line I6.

The effective shunt inductance at resonance of the line I6 is represented in the equivalent circuit of Fig. la. by a lumped inductance L1 having a. value required to tune the equivalent shuntresonant circuit Cji, L1 to resonance. The band Width of this resonant circuit, and the line I6, is determined by the equivalent shunt-damping resistance which appears across the circuit, this resistance being represented in Fig. 1a by the broken-line resistor R. For the equivalent circuitv diagram of Fig. la, it can be shown that the value of the effective shunt-damping resistor R for the conditions heretofor assumed is given b y the relation:

55. Where a`.=the distance in centimeters between the tap point, m andthe open end 22- of the line I6.

c=the velocity of light in centimeters per second.

Thev sharpness of resonance or band width of a resonant circuit is determined bythe ratio of energy stored inthe circuit to the energy dissipated therein and, for a shunt-damped paral- 65, lei-resonant circuit, therefore, is proportional to The band width. of a resonant circuit isy conventionally expressed with relation to the band width at those angular frequencies onl either side of resanswer onance'where the response ofthe circuit is three decibels below the Aresponsefat resonance. For

` this band width, they Q of the 'circuit is given by the relation:

where`Aw=the band widthat three decibles below the resonant response of the resonant circuit.

From Equations 3 and 4, it will be apparent that the band width has the value:

Substituting in Equationf5 the value of R given by kEquation 2:

Aw=gl2`R`a2 cos2 w-a (6) C1 a C Substituting the value of C1 from Equation 1 in Equation 6:

Aw=i canagliaa C052 n (7) Differentiating Equation '1 with relation tothe angular frequency and setting the differential equal to zero shows that the band width has a maximum value given by the relation:

Maximum band with is thus provided when the distance a between the tap point :z: and the open end 22 of the line I6 has the value:

where 1=the wave length of a wave signal having the resonant frequency to which the line I6 is tuned.

The value of wave length used in Equation 10 to determine the distance a preferably is that y value of wave length corresponding to the mean l or midband frequency of the range of frequencies over which the line I6 is tunable. `of the vdistance a, applicant has found that the For this value band width of the line I6 remains substantially constant over the tuning range of the line and that, on the other hand, the band width does not remain substantially constant for any other substantially different value of the distance a. It 3 may be noted that while the value of the distancev a for maximum band width is related to the selected wave length used in Equation 10, the actualy value of the maximum band width at this wave length is given by Equation 7 and consequently varies with the size of the coupling capacitance Ca, the characteristic impedance lR111 of the line I2 and the characteristic impedan-ce K of Jthe line I6. Thus, to establish any desired value of maximum band width, it is usually most convenient to choose the size of the conductive element 26 or its spacing from the inner conductor I9 of the line, or both.

It will be apparent from the foregoing discussion of Fig. la that thedistance a of the transmission line I1, and the valueof maximum band width, are similarly selected with relation to the wave-signal lwave length and the resistance component of impedance which is coupled by the coupling element 21 to the line I1 from that `circuit of unit I5 to whichv the line I1is coupled.

Fig. 1b representsthe equivalent circuit diagram ofthe coupled transmission'lines AI6 'and I1. L1 and C1 represent the circuit components of the parallel-resonant circuit equivalent to. the transmission line I6 as in Fig. la, while L2 and C2 represent the components of the .parallel-resonant circuit equivalent to the transmission line I1. The conductive elements 28 and 29, whichl are connected together bythe conductor 30 and are coupled to the respective inner conductors I9I and 2| of the respective transmission lines I6 and I1, provide an equivalent coupling capacitance Co which capacitively couples the transmission lines. In the following mathematical -analysisof the operation of these coupled lines, it is assumed that the lines are identical and are simultaneously tuned to the same wave-signal frequency. Thus, ofthe equivalentv circuit components, C1 is equal to C2 and L1 is equ-al to L2. It is further assumed that the coupling capacitan-ce C0v is very much less than the equivalent lumped capacitanceCi or C2 of either line. A

It can be readily lshown that the coefiicient of coupling lc between the transmission lines I6 and I1 is given by the relation: -v vwhere C=C1=Cz and has a value given by Equation 1.

b=the distance in centimeters between the tap point y and the open end 22 of either of the lines I6 or I1.

It will at once be apparent froml Equations 11 and 12 that the band width of the coupled lines I6 and I1 has the value: I I

l Aw'Koow @cs2 (18) When Equation 13` is, differentiated with respect to the angular frequency and the differential is equated to zero, it is-found that the band width has a maximum value given by the relation:

wb b"` f tan f= 1 j (14) Equation 14 is satisfied when:

7120.86 dans (15) or y b-o 862-0 vas-0 137 The values of wave length-used in Equation 16 in deriving the distance b is preferably, asin' deriving the distan-ce a by use of VEquation 10, a wave length corresponding to themeanor midband frequency of the frequency range over which the transmission linesIB and I1 are tunable. Applicant has found thatthis zvalue of the distance b ensures substantially constant band width-over the tuning range of the linesv I6 and I1 while any other substantially differentv4 value does not do so. The ,maximum band width of` the Lcoupled lines is given by Equation 13 and is preferably established by -choice of the size ofthe conductive `elements 28 and 29 vor their spacings from their respective kassociated inner conductorsY where m=the generalization of the'termsv a and l1,` and p=a constant being determinedby the characteristics of the coupled units, being equal to 3./'or l when used as in vlllquation 8 or 14 respectively.

Fig. 2 represents schematically .a Vmodified form of wave-signal selector .sy-stem essentially similar to either half of the'selector system of Fig. 1. For convenience of description, elements of Fig. 2 are designated lby reference numerals corresponding to those of similar elements of the line I6 to Fig. 1 and analogous elements are designated by similar refer-ence numerals primed. The'present selector systemdiffers from that of Fig. 1 in that the present system has its effective electrical length varied, to tune the system, by the provision of a-hollow inner conductor I9 for the ,transmission line I'BWith a conductive member'33 `arranged to telescope rin conductive relation into the lconductor I9. The adjusting member 25' of the present arrangement is of-dielectric-material. -It will be understood that the transmission line I6 vi-s shown only schematically andf-that the conductor I9' is suitably supported withinA the conductor I8 in insulated relation therewith; As thus arranged, the transmission line IB' is open circuited at its variableend 34 as well las its'fixed end 22. As is well known, such a transmission line vexhibits the characteristics-of r`an impedance transformer Vin'that it transforms the high impedance-at itsopen end 34 to, alowimpedance at a region Z spaced one-quarter wave length distant from its open end r34. 'It will 'be apparent that the region-Z moves 'longitudinally of the line I 6' with longitudinal adjustment of the conductive member 33so that the -lowimpedance at this region has the ysame effect and is the full equivalent of the conductive shorting member A23 of the Fig. 1 arrangement. The operation ofthis modified form of the invention is otherwise essentiallysimilar'to that of Fig. 1 and will not be repeated.

An additional modified form lof the .invention which utilizes inductive coupling, in contradistinction to 'the capacitive coupling employed in the Figs. 1 and 2 arrangements,` is illustrated :in Fig. 3. Aside from the manner of coupling,1the instant wave-signal selector system is essentially similar to that of Fig. 1, similar elements being designated .by similar reference numerals and analogous elements/by similar reference numerals-double primed. In the instant arrangement, the inner conductors I9 and 2|" ofr the respective lines I6 and I1 are extended into conductive engagement with the conductive discs 3|, 3| whichclose the lines. Additionalljnthe lines |6" and Il are adjustable by movablemembers 23 and 24 to have an eiective electr-ical length of an integral number of half-wave lengths at the lowest frequency of the operating frequency range of the selector system I3. As earlier mentioned, inductive coupling is employed in the presentselector system. To this end, the transmission line I2 is'terminated by'an inductive coupling loop 3G "positioned withinthe line I 6"' and spaced a -distancee from' `the fixed short-circuited end" 22 "of theline; the transmission line I4' is similarly terminated lin an inductive coupling loop 3l positioned within lthe line land spaced a distance e from .the fixed short-circuitedend 22 thereof; .and the conducto-r 30 is terminated at one end by Aan inductive coupling loop 38 located Within the line I6 and spaced ka distance f from the-fixed short-circuited end 22" of the latter and is terminated at its other `end by a similar inductive coupling loop -39 lying within the line Il and likewise spaced a distance f from fthe fixed` short-circuited end 22"'0f the latter.

From the principle of duality, it will be apparent that the .arrangement of the Fig. `3 selector system is essentially the inverse electrically ,of that of Fig; 1 and hence, that their operationsare similar. The principle of duality is applicable-to inverse electricalnetworks asmore fully explained in Communications Networks, volume- II, page 246 et sequa, -by E. A. Guillemin, vpublished by John Wiley `and Sons vof `New York (copyright 1935). Briefly considered,the principle of duality proceeds from the recognition that the .behaviorof'an electrical network may ibe-.expressed either -as the current response to an impressed voltage or as a voltage response toan impressed current. In usi-ng this principle, two electrical networks are the..inverse of one another when the currents and magnetic ields in one circuit can be replaced .by equivalent voltages and .electrical elds at corresponding points in the second circuit, when the inductances and capacitances 0f one circuit are interchanged with equivalenticapacitances and inductances, respectively, in vcorresponding positions in the second circuit, when the resistances in one circuit are ,replaced by equivalent conductances .in the secUndcircuit, when series and parallel `branches :of one circuit are replaced by parallel `and series branches, rrespectively `in the second circuit, and when `short circuits and open circuits ofthe one circuit vare replaced by .open circuits and short circuits, respectively,in the other circuit.

.Applying this principleto Figs. 1 and 3, itl will be noted athat'the capacitive couplings of Fig. 1 which intercouple the electric fields in several portions :of theFig. lselector system are replaced by inductive couplings which intercouple the magnetic iields of=corresponding portionsof the lFig. 3 selectorsystem. Similarly, the ylines I6 and I1, open-circuited and having high impedances at their ends 22 in Fig. l, are replaced by corresponding lines shortcircuited and having low impedances yat theirs ends 22 in Fig. 3. Likewise, while the maximum voltages occur at the -open ends 2-2 of the lines |f6 and Il of Fig. 1,the maximum currents occur at the shorted ends 22" of thelines IB" and Il in Fig.-3. Furthenwhereas the lines |16 l and I1 are short-circuited by the respective piston members 23 and 24 and thus have low impedance one-quarter wave -lengthdistant from their open-circuited-'ends 22, the lines I6" and 'I" are open-circuited and have-maximum impedances at a point one-quarter wave length from their short-circuited ends 22". Thus, since'the Figs. 1 and 3 arrangements are the full inverse of one another, the distances e between the -coupling loops 3B and 31 of the respective lines I6" and I'I and the short-circuited ends 22 of the latter are the same as the distances ,a of the corresponding points of coupling in the Fig. lfarrangernent. Likewise, thedistancesf belll' thevFigi-S arrangement have the same values as the yspacings b between the corresponding points rif-coupling and the open ends 22 of the lines in theFigQ-.l system. The spacings e and f may thus be evaluated -by a mathematical analysis similarto; that explained above in connection with the 'Fig` 1 arrangement or 'the values may be derived for-a selector system of the Fig. 1 type and may thenbe'used for-asystem of the Fig. 3 type. The operation of the Fig.-3'selector system is other- Wise essentially similar to that described in connection with Fig. 1 and will not be repeated.

Fig. 4 schematically represents a modified form of `Wave-signal selector system essentially similar tothe Fig. 3 system except that the instant arrangement utilizes a re-entrant type of coaxial transmission lone 4I The line 4|, which Imay be inductively coupled' in tandem if ldesired with one or `more similar such lines as in the Fig. 3 arrangement, includes anl outer conductor 42 having its ends closed by a conductive member 43 anda conductive member 44 coaxially apertured at'45. The edges of the aperture 45 are formed as y'resilient fingers which conductively engage an axially movable inner coaxial conductor'46, the latter being arranged in telescopic relation with, but spaced from, the inner surfaces of a hollow coaxial conductor 4l electrically connected to the conductive member 43. Two inductive coupling loops? 48 and 49 couple the selector system to Wave-signal translating apparatus external thereto. The transmission line 4I as thus arranged is of a type disclosed in a copending application of Harold A. Wheeler, Serial No. 565,829, led November 30, 1944, entitled Transmission-Line Section, now abandoned, and assigned to the same assignee as the present application. This line is essentially short-circuited at one end, open-circuited at the other, and has an eiective electrical length equal to an odd number n ofv quarter wave lengths as indicated, the electrical length of the line being varied `for tuning purposes by `axial movement of the conductor 46 thereof. The operation of this modified form of the invention is otherwise essentially similar to that described in connection With Fig. 3 and Will not vbe repeated.

Fig. 5 represents schematically an additionally modied form of selector system embodying the invention. This system utilizes a coaxial transmission line 5| including an outer conductor 52 and a' coaxial inner conductor 53 having a telescopic extensible end portion 54 to vary the eifective electrical length of the conductor 53 for tuning purposes. The adjusting member 25 is of dielectric material. Inductive coupling'loops 56 and 51, located individual xed distances from the short-circuited end of the line, are utilized to couple the selector system to external Wavesig'n'al circuits, not shown. The elective electrical length -of the line 5l, is equal to an odd number n vof.quartervvave lengths as indicated, the electi'ricallengthl of the line being varied for tuning purposesby axial movement of the conductor`54 thereof. The distances of the coupling loops 56 and lfromthe short-circuited end of the line are selected as explained in connection with Fie. 3 `to'attain a desired value of constant band width for the selector system over the tuning range thereof. The operation of this modified form of the invention is otherwise essentially similarI to that of Figs. 3 and 4 and will not be repeated. Fig. 6 illustratesa form of the presentinveni tion as applied to .al rectangularwave guide 58 having awidth w and height hselectedlin con-l ventionallmannerf t-oaeffectiia 'desired vmode of.

wave-signal propagationj Arconductive vaneL4 member 59, positioned Awithin the rwave guide 58 andhaving contactngers-G around the periphery thereof to engagerthe inner surfaces of the wave guide, tunes-the resonant waveguide in conventional manner, the -vane 59 being adjusted longitudinally of the waveguide by a suitable adjusting member 6l mechanically coupled thereto. An inductive coupling member 62 is positioned within the, resonantvchamber of the wave guide and is connected 'gat"onel 'end' to' the 'inner'con-- ductor 63 of a*coaxial,transmission'line 64, which couples the wave gui'detoY Kanfe'xternal wave-signal apparatus, not show'n, and. is connected 'at its other end tothe opposite side of the wave guide 58 as shown. The diameter of the coupling member 62 is,preferably-sufciently'large that its inductive'reactance is much-smaller than the characteristic impedance of lthe line 64. In this arrangement, the distance Z of the vane 59 from the closed endof the Wave guide 58 determines the resonant frequency. ofthe Wave guide, the distancel 4being slightly more than one-half wave length :at the frequency Vof a desired wave-signal to be translated by thewave guide. Where the Wave guide58 is operated in a mode, such as the TE1,o mode in a rectangular waveguide, having thesame sinusoidal magnetic andelectric field distributions Eas inthe coaxial transmission lines previously describedin connection with Fig. 3, the distance t of theinductivevcoupling member 62 from the xed closedend o-f thev wave guide is selected to attainconstant band width of the selector system in the same manner as described above with relation to Fig. 3;- In this connection, it shouldv bejborne` in mind that a region of maximum wave-signal impedance is developed along a plane transverse the wave guide and spaced one-quarter wave length from its closed end thus corresponding-to the region of maximum wavesignal impedance developed near the center of each of the transmission lines of Fig.3. In the present arrangemenarthespacing sof the coupling member l62 from thesidegoi the Wave guide 58 is also elective to ydetermine the magnitude of inductive coupling, and. thus the mean band width of the selector system r`over its range of adjustment.

While the Fig. 6 typeof Wave-signal selector system hasbeen shown as utilizing a single inductive coupling member, it will be apparent that a plurality of such ,inductive Vcoupling members may be utilized as in the Fig. 3 selector system. Furthermore, it will be apparent that two or more such wave guides of the Fig. 6 type may be inductivelycoupled in tandem in accordance with the principles hereinbeforeldescrib'ed.

While there have been described what are at present considered to vbe the preferred embodiments of this invention,'it will be obvious vto those skilled in the art that various changes and modications may-be made thereinwithout departing from the invention,l and it is, therefore, aimed in the appended claims to cover all such changes and modifications as fall-withinthe true-spirit and scope of the invention.

What is claimed-is: l-' 1- A 1. A Wave-signalselector lsystem adjustable over'avgivenrelatively wide frequency range comprising: a' resonant-wave guide-having a frequency pass-*band of predetermined Y.band Width vand adapted to" be'coupled 'toy an electrical device;`

13r means for adjusting the eiective electrical :length of said wave guide to tune said selector'system over said frequency range; and wave-Signal coupling means electrically coupled to said wave guide at a point along the length thereof and adapted to` provide said coupling between said Wave guide `and a resistance component of impedance provided by said device effective to increase said band width of said Wave guide, the location of said coupling point being'determined by the relation Ttan c -p where e represents the angular frequency in radians per second of the signal in said wave guide lat resonance, `c represents the Velocity of light in centimeters per second, 'm represents the distance in centimeters between said coupling point :and one end of said wave guide, and p is a constant having a value determined by the characteristics `of said lwave guide and said device, whereby said selector system has, for a constant value of said resistance component of impedance, asubstantially constant band Width for any adjustment within said range.

2. A wave-signal selector system adjustable over `a given relatively Wide frequency range comprising: a wave guide having at least one end on open circuitand frequency pass band of predetermined band width and adapted to be coupled 14. vice effective to increase said band width of .said wave guide, the location-of said coupling point being determined at a fixed kdistance from .said first region by the relation where w represents the angular frequency in radians` per second of the signal in .said wave guide at resonance, c represents the velocity of v light in centimeters per second, m represents said to an electrical device; means for adjusting the effective electrical length of said Wave guide to tune said selector system over said frequency range; and wave-signal coupling means capaci tivelycoupled to said wave guide at a point along the length thereof and adapted to provide said coupling between said `wave guide and a resistance component of impedance provided by said device effective to increase said band width fof said wave guide, the location of said coupling point being determined at a fixed distance from said 'one end of said wave guide by the relation gmtan where c represents the angular frequency in radians per second of the signal in said Wave guide at resonance, c represents the velocity of light in centimeters per second, m represents the distance in centimeters between said coupling point and said one end of said Wave guide, and p has a value of 1 or determined by the characteristics yof said Wave guide and said device, whereby said selector system has, for a constant value of said resistance 'component of impedance, a. substantially constant band width for any adjustment within said range.

3. A wave-signal selector system adjustable over a given relatively Wide .frequency range comprising: a resonant wave guide having a first fixed region of maximum wave-signal impedance and a frequency pass band of predeterfixed distance in centimeters, andp has a value of 1 or 3/2 determined lby the characteristics of said wave guide andrsaid device, whereby said selector system has, for -a constant value of said resistance component of impedance, a substanf tially constant band width for any adjustment within said range. f

4. A Wave-signal selector system adjustable over a given relatively wide frequency range comprising: a resonant 'Wave guidehaving a xed region of maximum wave-signal impedance and a frequency pass band of predetermined band width and adapted to be coupled to an electrical device; conductive means movable longitudinally of said wave guide for terminating the electromagnetic eld thereof to adjustthe -effective electrical length of said wave guide to tune .said selector system ovel` said frequency range; and Wave-signal coupling means `capa'citively coupled to said Wave guide at a point along the length thereof intermediate said region of maximum impedance and said conductivemeans and adapted to couple thereto a resistance component .of impedance provided .by said device'effective to increase said band width of said wave guide, the loction of said coupling point being determi-ned at a flxed distance from said regioniof maximum impedance by the relation c au c p v where w represents the angular frequencyin radians per second of the signal in said Wave guide at resonance, c represents the velocity of lightin centimeters per second, m represents said fixed distance in centimeters, and p `has a value of 1 or 3/2 determined by the characteristics of said wave guide and said device, whereby said selector system has, for a constant value of said resistance component of impedancaa substantially constant band width for any adjustment Within said range.

5. A wave-signal selector system adjustable over a given relatively wide frequency range comprising: a resonant Wave guide of the coaxial transmission type having a fixed region of maximum wave-signal impedance and a frequency pass band of predetermined band Width and adapted to be coupled to an electrical device; a conductive member adjustable,longitudinally of said line to provide at said member a region of minimum wave-signal impedance to tune said selector system over said frequency range, and wave-signal coupling means Icapacitively coupled to said transmission line at a point along the length thereof and adapted to couplethereto a resistance component of impedance provided by said device effective to increase said bandwidth of said transmission line, the location of said coupling point being determined at a fixed distance from said region of maximum impedance by' the relation l Tian fr prising: a resonant wave guide having at least one closed end and a frequency pass band of predetermined band width and adapted to be coupled to an electrical device; means for adjusting the effective electrical length of said wave guide to tune said selector system over said frequency range; and wave-signal coupling means inductively coupled to said wave guide at a point along the length thereof and adapted to couple thereto a resistance component of impedance provided by said device which is eiiective to increase said band width of said Wave guide, the location of said coupling point being determined at a fixed distance from said closed end of said Wave guide by the relation v "t l.

cy an c p where w represents the angular frequency in radians per second of the signal in said wave guide at resonance, c represents the velocity of light in centimeters per second, m represents said fixed distance in centimeters, and p has a value of 1 or 3/2 determined by the characteristics of said wave guide and said device, whereby said selector system has, for a constant value of said resistance component of impedance, a substantially constant band Width for any adjustment Within said range.

'7. A Wave-signal selector system adjustable over a given relatively wide frequency range comprising: a resonant wave guide having a fixed region of minimum wave-signal impedance and a frequency pass band of predetermined band width adapted to be coupled to an electrical device; means co-operating with another region of said wave guide spaced from said rst-mentioned region for providing a second adjustable regiorf of high wave-signal impedance to tune said selector system over said frequency range; and wave-signal coupling means inductively coupled to said wave guide at a point along the length thereof intermediate said first-mentioned and second-mentioned regions and adapted to couple thereto a resistance component of impedance provided by said device which is effective to increase said band width of said wave guide, the location of said coupling point being determined at a, fixed distance from said region of minimum impedance by the relation c 81D c p where w represents the angular frequency in radians per second of the signal in said wave guide at resonance, c represents the velocity of light in centimeters per second, m represents said fixed distance in centimeters, and p has a value of l 0r 3/2 determined by the characteristics ofV said Wave guide and said device, whereby said selector system has, for aA constant value of said resistance component'of impedance, a substantially constant band width for any adjustment Within said range.,

v8. Av Wave-signal `selector system adjustable over a given relativelyA wide frequency range comprising; a resonant wave guide closed at one end having anv electrical length approximately equal to an integral number of half wave lengths at the frequency of resonance thereof and a frequency pass band of predetermined band width and adaptedto be coupled to an electrical device; conductive means lclosing the other end of said Wave guide and movable longitudinally thereof to tune said selector system over said frequency range; and wave-signal coupling means inductively coupled to said wave guide at a point along the length thereof and .adapted -to couple thereto a resistance componentof impedance provided by said device which is effective to increase said band width of said wave guide, the location of said coupling point being determined at a fixed distance from s-aid one end of said wave guide by the relation ft M c an c p where w represents the angular frequency in radians per second of the signal in said wave guide at resonance, c represents the velocity of light in centimeters per second, m represents said fixed distance in centimeters, and p has a value of 1 or 3/2 determined by the characteristics of said wave guide and said device, whereby said selector system has, for a constant value of said resistance component of impedance, a substantially cons-tant band width for any adjust'- ment within' said range.

9. A wave-signal selector system adjustable over a given relatively wide frequency range comprising: a plurality of resonant wave guides; means for adjusting the effective electrical lengths of said wave guides to tune said selector system over said frequency range; and wave-signal coupling means electrically coupling said guides at a point along the length of each thereof; the locations of said coupling points being determined by the Vrelation where o represents the angular frequency in radians per second of the signal in each of said wave guides at resonance, c represents the velocity of light in centimeters per second, and b represents the distance in centimeters between each of said lcoupling points and the end of each of said Wave guides oppOsite said adjusting means, whereby said selector system has a substantially constant over-all bandwidth for any adjustment within said range.

10. A Wave-signal selector system adjustable over a given relatively wide frequency range comprising: a plurality of resonant wave guides; means for simultaneously adjusting the effective electrical lengths of said Wave guides to tune said selector system over said frequency range; and wave-signal coupling means electrically coupling said wave guides at a, point along the length of each thereof; the locations of said coupling points being determined by the relation ltan c"-b=l c l c where w represents they angular frequency in radians per second of the signal in each of said wave guides at resonance, c represents the velocity of light in centimeters per second, and

atrapar lrf represents the distancefin centimeters between .eachof said'` coupling; pointsandtlie end of; each rof, said: waveiA guides opposite said. adjusting means,vwherebyfsaid selector system. has va sub'- stantially constant,v overeall band widtlizfor. any 'adjustment within said range.

l-l. `A Wave-signal selector 'system/ adjustable over a given relatively w'ide'frequency range region of minimum lWave-signal impedance to tunefsaid selector system over said frequency range; and wave-signal coupling means capacitively'coupling saidwave guidesfat a pointalo'ng the length of eachA thereof `the locations -f o'fl said coupling points being determined at a xe'd di'stance: from said regions of maximum impdance by the relation Where w represents the angular frequency in radians per second of the signalin each of said Wave guides at resonance, c represents the velocity of light in centimeters per second, and b represents said fixed distance in centimeters, whereby said selector system has a substantially constant over-all band width for any adjustment Within said range.

12. A wave-signal selector system adjustable over a given relatively wide frequency range comprising: a plurality of resonant wave guides each having a fixed region of maximum wavesignal impedance; conductive means terminating the electromagnetic neld of each of said wave guides and adjustable longitudinally thereof to tune said selector system over said frequency range; and wave-signal coupling means lcapacitively coupling said wave guides at a point along the length of each thereof; the locations of said coupling points being determined at a fixed 'distance from said regions of maximum impedance 3y the relation Where w represents the angular frequency in radians per second of the signal in each of said wave guides at resonance, c represents the velocity of light in centimeters per second, and b represents said xed distance in centimeters, whereby said selector system has a substantially constant over-all band width for any adjustment within said range.

13. A Wave-signal selector system adjustable over a given relatively Wide frequency range comprising: a plurality of resonant Wave guides each having at least one closed end; means for adjusting the effective electri-cal lengths of said wave guides to tune said selector system over said frequency range; and Wave-signal coupling means inductively coupling said Wave guides at a point along the length of each thereof; the locations of said coupling points being determined at a fixed distance from said closed ends of said wave guides by the relation where w represents the angular frequency in radians per second of the signal in each of said waveguides at resonance',` c; represents-the velocity? of light inl centimeters per second, and Z represents saidfxed dis-tancev in centimeters, whereby said selector system has a substantially constant over-allband width for any adjustment within said range.:v '1

14. A wave-signal selector system adjustable overa given relatively' Wide' frequency range comprising a' plurality ofresonant wave guides each having a fixed regionv of minimum Wave-signal impedance; tuning mea-ns cli-operating with another' region' of each of said guides'y spaced from said reg-lon rif-minimum impedance for providng in each' thereof vai` second adjustable region of maximum wav'ee'signal impedance to tune said se lector syst'en'iover Vsaidv frequency' range; and wave-'signal coupling' means ri'nductively coupling said Wave guides at a pointA along the length of each thereof intermediate said high-impedance and low-impedance'regicrisj the locations of said coupling points` being. determined at a xed d istance from said regiens of" m`inixrmmr impedance by the relation where a represents the angular frequency in radians per second of the signal in each of said Wave guides at resonance, c represents the ve locity of light in centimeters per second, and b represents said fixed distance in centimeters, whereby said selector system has a substantially constant over-all band width for any adjustment Within said range.

15. A wave-signal selector system adjustable over a given relatively wide frequency range comprising: a plurality of resonant wave guides each closed at one end and having an electrical length of approximately one-half Wave length at the frequency of resonance thereof; conductive means closing the other end of each of said wave guides and adjustable longitudinally thereof for adjusting the effective electrical lengths of said Wave guides to tune said selector system over said frequency range; and wave-signal coupling means inductively coupling said Wave guides at a point along the length of each thereof; the locations of said coupling points being determined at a fixed distance from said one end of said wave guides by the relation Where w represents the angular frequency in radians per second of the signal in each of said wave guides at resonance, c represents the velocity of light in centimeters per second, and b represents said fixed distance in centimeters, whereby said selector system has a substantially constant over-all band Width for any adjustment Within said range.

16. A wave-signal selector systme adjustable over a given relatively wide frequency range com-` prising: a plurality of resonant Wave guides each having a frequency pass band of predetermined band Width and adapted to be coupled to one another and to an electrical device; means for adjusting the effective electrical lengths of said wave guides to tune said selector system over said frequency range; a plurality of wave-signal coupling means electrically coupled to individual ones of said Wave guides at a first point along the length of each thereof and adapted to provide said coupling between said wave guides and individual resistance components of impedance provided by said device eiective to increase said band Width of said individual wave guides, the

locations of said firstv coupling pontsbeing determined by the relation ma wa, 3.

Tian 7:5

Where w represents the angular frequency in radians per second of the signal in each of said wave guides at resonance, c represents the velocity of light in centimeters per second, and a represents the distance in centimeters between each of said coupling points and one end of said Wave guides; and Wave-signal coupling meansl electrically coupling said wave guides at a second point along the length of each thereof, the locations of said last-mentioned points being determined by the relation f cob Where w and c represent above-mentioned charfro :'acter'istics of said Wave guides at resonance, and

b represents thedistance in centimeters between .each of said second predetermined points and one end of each of said Wave guides, whereby said wave guides, for constant values of said individua1 resistance components of impedance, and said selector system have substantially constant band width for any adjustment within said range.v

BENJAMIN F. TYSON.

REFERENCES CITED The following references are of record in the iile of this patent:

UNITED STATES PATENTS 

